[gnome-flashback] system-indicators: avoid critical warning

[Alberts Muktupāvels <muktupavels src gnome org>]

commit 059c7214b0a621f13e6659cf18988c04604d8919
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Fri Dec 27 21:40:16 2019 +0200

    system-indicators: avoid critical warning

 system-indicators/si-volume.c | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/system-indicators/si-volume.c b/system-indicators/si-volume.c
index a6cc6d0..27a1b9c 100644
--- a/system-indicators/si-volume.c
+++ b/system-indicators/si-volume.c
@@ -644,6 +644,9 @@ get_has_headphones (SiVolume *self)
       g_strcmp0 (form_factor, "headphone") == 0)
     return TRUE;
 
+  if (gvc_mixer_stream_get_ports (self->stream) == NULL)
+    return FALSE;
+
   port = gvc_mixer_stream_get_port (self->stream);
 
   if (port != NULL && g_strstr_len (port->port, -1, "headphone") != NULL)